1. Field of the Invention
This invention relates to miniature switches for use in electrical circuits, and more particularly, to miniature push button electrical switches that exhibit quiet operating characteristics for minimizing noise production.
2. Description of the Related Art
In the field of electrical switch design, audible noise often results from the operation of the switch mechanism and varies with the type of switch mechanism used. While some designs achieve noiseless operation (such as clamp type or mercury switches), most types of switches produce audible noise due to the mechanical construction. Efforts have been expended to quite down the operation of some of these designs. A reinforced or modified switch designed to accommodate a higher current carrying capacity generally produces higher levels of audible noise. An example of an application of an electrical switch that normally produces a high level of audible noise is a typical commercial or residential wall mounted light switch. Certain manufacturers have designed wall mounted light switches which produce a lower level, although as to an inaudible amount of noise, and such switches are available for use in the construction industry.
The decision whether to use a high audible noise switch or a low audible noise switch is subjective. A more relevant example exists in the electrical switches employed in the cabin of expensive motor cars. Some manufacturers prefer that the switches employed produce low audible noise levels to be consistent with the mood created by the luxury coachwork. Conversely, many European automobile manufacturers choose to employ a heavy duty electrical switch within the cabin which produces a high level of audible noise.
Electrical switches are also normally employed in consumer appliances. Because of electrical installation standards required by the National Electric Code, appliances are often designed with two layers of plastic insulation referred to as "double insulation". By employing double insulation in the manufacture of electrical appliances, the use of ground wire conductors may be dispensed with since the threat of electrical shock is reduced. The plastic construction of the appliance not only insulates the electrical circuit contained within the appliance, but also acts as a sounding board for the absorption of the audible noise produced by the electrical switch. Switch construction employed in electrical appliances normally produce high levels of audible noise.
In the past, the construction of a switch displaying quiet switching action has been accomplished in a small number of switch types. A first example of such a quiet switch-type is a "disc mechanism" switch which is available in manual or automatic designs. An example of the "disc mechanism" switch may be a rotating switch device having a plurality of contacts with each contact located at the end of an individual finger. The fingers may be connected to the central disc mechanism which is rotated on a periodic basis and which may be controlled by a computer program. The contacts located at the end of the fingers may pass through a narrow space which includes a stationary contact connected to electrical circuitry.
During the period of time that one of the plurality of fingers is located in the narrow space, the first finger contact and the stationary contact are in communication completing an electrical circuit. Upon manual or automatic operation, the disc mechanism may be rotated causing the contact located at the end of the first finger to break communication with the stationary contact located within the narrow space. Electrical communication with the next contact located at the end of the next finger rotated into position is then made with the stationary contact located in the narrow space.
A second type of quiet switch developed by designers in the past is the "heart and bail" switch. This type of switch is normally employed in telephone switchboards and is a spring-cam operated switch. The cam has the characteristic shape of a heart while the bale is a wire which limits the travel of the spring operated switch. The "heart and bail" portion of the switch is mechanical in nature and is not associated with the electrical switching portion Although the "disc mechanism" switch and the "heart and bail" switch are generally quiet switches, their application is limited, particularly with respect to the current carrying capacity.
A third type of quiet switch developed in the past is the "membrane switch". The membrane switch is also associated with telephone equipment and is of the type normally found on a telephone keyboard employed as a dialing switch. In dialing a telephone, the membrane switch is employed for transmitting intelligent information at signal levels in the microamp and milliamp range. As with the previous quiet switch designs, the membrane switch is also current limited restricting its usage.
A type of push button switch typically capable of accommodating relatively high electrical currents is one employing a ratchet mechanism. Depression of the plunger of such a switch causes an electrical switching member to alternately make and break the electrical contacts in the switch. The ratchet mechanism of such switches makes a distinctive "clicking" sound as the mechanism is operated and, as discussed above, the "clicking" sound can be undesirable for certain applications. Further, certain problems unique to ratchet mechanism type switches must be considered when incorporating means to quiet the operation. Because ratchet switches employ wire coil springs damage to the internal structure of the switching device can occur when the ratchet mechanism rotates in a direction opposite to the direction to which the spring is wound.
Still another problem unique to ratchet switches is that when the point of contact between the teeth of the switch plunger are directly aligned opposite to the teeth of the ratchet mechanism, the ratchet mechanism can misalign upon operation preventing positive engagement of the teeth and causing the ratchet not to rotate. The misalignment and failure to rotate causes the ratchet switch to remain in a single position. The end result is that the electrical contacts of the device are not switched.
Additionally, the current carrying capacity of such a switch must not be compromised in the effort to quiet the operation by perhaps reducing the contact separation during the open circuit position or reducing the contact engagement force during the closed circuit position. Thus, it is desirable that any methods used to quiet such switches do not impact the basic functions and advantages of the switch and its ability to carry the desired current.
Hence, those concerned with the development and use of quiet switches in the electrical construction field have long recognized the need for improved miniature switching systems which reduce the audible noise level during operation, have higher current carrying capacities while utilizing standard parts of the existing ratchet switch, are capable of switching multiple circuits, prevent misalignment of the ratchet teeth and misoperation of the switch, and which minimize wear thereby extending the life of the switch. The present invention fulfills all of these needs.